Infections bite! Antibiotic prophylaxis for mammalian bites

This is part of a recurring series examining landmark articles in Emergency Medicine, in the style of ALiEM’s 52 Articles.

Discussing:  Medeiros, I, and H Saconato. “Antibiotic prophylaxis for mammalian bites.”  Cochrane database of systematic reviews Online 2 (2001) : CD001738.

Main Points:

  1. The use of antibiotic prophylaxis for hand bites reduces infections
  1. There is weak evidence supporting the use of antibiotic prophylaxis after human bites to reduce infections (based on one study)


Mammalian bites account for up to 1% of all ED visits and administration of prophylactic antibiotics is based on studies with insufficient power to determine true efficacy. In order to gather enough cases to sufficiently power a study, The Cochrane Collaboration did a meta-analysis of randomized trials considering the value of antibiotic prophylaxis in human and other mammalian bites. The goal of this analysis was to determine if the use of antibiotics in mammalian bites is effective in preventing bite wound infection.

Eligible studies were searched and retrieved based on inclusion criteria (see details) by two reviewers. Relevant data to answer the study question were extracted, risk of bias was assessed for included studies, and subgroup analysis was performed based on intention to treat of the eight final studies chosen.

For dog bites, there was no statistically significant reduction in infection rate after prophylactic antibiotics (4% (10/225)) versus control (5.5% (13/238)). Only one trial analyzed human bites and the infection rate was significantly lower in the antibiotic group (0/33) versus the control group (47% (7/15)) (OR 0.02, 95% CI 0.00 to 0.33). The infection rates for hand bites were significantly reduced by antibiotic administration (2% vs. 28% in control group) (OR 0.10, 95% CI0.01 to 0.86, NNT=4, 95% CI 2 to 50). There appeared to be no significant difference in infection rate with antibiotic prophylaxis for cat bites, when separating out wound type (laceration vs. puncture), or for bites on body parts other than the hand.

Pitfalls of this meta-analysis:

  1. The antibiotics chosen for prophylaxis were not consistent across studies, and no more than two studies used the same antibiotic. In some studies, the antibiotic used was inappropriate for coverage of mixed anaerobes and aerobes, which is common in many mammalian infections.
  2. The predominance of included patients suffered dog bites (463/522) compared to cats (11/522) or humans (48/522), so the results are skewed heavily toward one species of bite.
  3. Only five studies reported LTFU and three of these had rates over ten percent. Four studies did not even include LTFU numbers, and an intention to treat analysis could not be performed in these. This may bias the results toward no effect since those who did not go on to have an infection would likely not return to the ED.
  4. Only 25% of the studies used double-blinded methods with a placebo of identical appearance.


This was a meta-analysis study, with the following inclusion criteria:

  1. Study type: RCTs or quasi-RCTs
  2. Participants: patients with mammalian bites (including humans) if they presented within 24 hours and had no clinical signs of infection.
  3. Interventions: use of antibiotics within 24 hours of injury compared to placebo/no-intervention.
  4. Outcomes measured: proven bacterial infection (clinical signs of infection plus positive culture), presumed infection (clinical signs of infection with negative culture) or absence of infection (no clinical signs).

Nine studies met all inclusion criteria but one study did not separate infection rates for each mammalian species.

Level of evidence:

ACEP Level I for Meta-analysis

Source article: Medeiros, I, and H Saconato. “Antibiotic prophylaxis for mammalian bites.” Cochrane database of systematic reviews Online 2 (2001) : CD001738.


1 thought on “Infections bite! Antibiotic prophylaxis for mammalian bites

  1. I agree – numbers are so skewed that it’s difficult to say anything about cat or human bites from this. And, I’ll say this about cat bites – if no signs of infection at 24 hours, it’s probably going to be ok. When they come in 4 hours later with pain, swelling, redness, po abx are probably not going to do the trick.

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